[6.x] Hash URL in static caching lock key (#14716)

Author: duncanmcclean

src/StaticCaching/Middleware/Cache.php

@@ -241,7 +241,7 @@ private function createLock($request): Lock
             $store = AppCache::store('null');
         } else {
             $store = StaticCache::cacheStore();
-            $key .= '-'.$this->cacher->getUrl($request);
+            $key .= '-'.md5($this->cacher->getUrl($request));
         }
 
         return $store->lock($key, $this->lockFor);